Wireless communication systems are in widespread use for a variety of applications. Perhaps the best known wireless system architecture is the frequency reuse design, commonly referred to as cellular. Cellular systems have traditionally been used to provide telephone interconnect service, providing a mobile station with a wireless interface to the public switched telephone network, but more recently additional types of communications services are being provided in cellular systems, and with newer interface protocols and modulation schemes.
In frequency reuse or cellular systems, a serving cell is established in the local vicinity of a base station. An array of base stations provide service coverage over a region which may be a small metropolitan area or a state wide network. Adjacent cells are referred to as neighbor cells, and as a mobile station travels from one serving cell to the next, the service is handed off from the serving cell's base station to the neighbor cell's base station, and the neighbor cell becomes the serving cell for the mobile station. This scheme allows the reuse of radio frequencies in a metropolitan region since the power of the base station's transmitter is usually very low compared to other types of broadcast service.
In a typical cellular network, the base stations of a given region are operably coupled via a communications link to a communications server in a central office. Traditional cellular telephone systems have a mobile switching center as a communications server to provide telephone interconnect service. More recently other types of communication service have been offered, such as, for example, dispatch service, which is sometimes referred to as direct connect. For each type of service a different communications server is typically used, or a more conventional communications server is fitted with additional hardware and software to provide additional functionality.
The communications link between the base station and the communications server(s) is typically terrestrial plant, such as a hybrid fiber/coaxial cable network, for example. Signals may be carried to and from the base station by any one of several common and well known protocols, such as frame relay or SS7, for example. If more than one service is provided by a base station, then there is typically a dedicated communications link between the base station and each communications server.
Communications links carried over terrestrial plant are susceptible to faults, resulting in a disruption of service. Faults occur when, for example, in-line regenerative amplifiers fail or when cables are knocked out of service. One way to avoid service outages is to set up redundant communications links between the base station and the communications servers, each of the links using a different physical path between the base station and the communications servers. When a fault is detected on the active communications link the system switches to the redundant link.
However, installing and maintaining a multi-path redundant network plant is a considerable and on going expense for a network operator. In many networks, it is often the highest operating expense. Furthermore, the circumstances that create the failure of a first communications link may very well affect other links, including redundant links. For example, in northern climates winter storms can cause substantial damage to terrestrial based communications links. Even with multi-path redundancy, when multiple failures occur, mobile stations are not informed with current neighbor cell information, and cannot determine if a neighbor cell can provide the desired service. Therefore, there is a need for a means by which fault tolerance may be provided in a wireless frequency reuse communications system wherein mobile stations receive current neighbor cell information updates.